U.S. patent number 4,565,553 [Application Number 06/614,101] was granted by the patent office on 1986-01-21 for method for the removal and disposal of paint solvent.
Invention is credited to William C. Nowack.
United States Patent |
4,565,553 |
Nowack |
January 21, 1986 |
**Please see images for:
( Certificate of Correction ) ** |
Method for the removal and disposal of paint solvent
Abstract
An industrial painting method and system utilizing a washer,
dry-off oven, spray booth, and bake oven, in which solvent paint
vapors from the spray booth are concentrated in a filter which is
subsequently degassed by a flow of hot air from the dry-off oven,
and the degassed vapors admixed with the atmosphere of the bake
oven. The bake oven atmosphere is continuously circulated to the
washer and burned in the burner of the washer to incinerate solvent
vapors, and the gasses produced by incineration are transported to
the dry-off oven to form the atmosphere thereof. The principal
exhaust from the system occurs from the dry-off oven and is
substantially free of solvent vapors and of low temperature.
Inventors: |
Nowack; William C. (Twin Lakes,
WI) |
Family
ID: |
24459874 |
Appl.
No.: |
06/614,101 |
Filed: |
May 24, 1984 |
Current U.S.
Class: |
95/141;
34/DIG.1 |
Current CPC
Class: |
B01D
53/04 (20130101); B01D 53/0407 (20130101); B05B
16/90 (20180201); B05B 16/20 (20180201); B01D
2253/102 (20130101); B01D 2257/704 (20130101); B01D
2259/402 (20130101); Y10S 34/01 (20130101); B01D
2259/4009 (20130101) |
Current International
Class: |
B01D
53/04 (20060101); B05B 15/12 (20060101); B01D
053/04 () |
Field of
Search: |
;34/32,40,43,80,82,DIG.1
;55/18,20,59,62,74,88,89,161,179,180,208,387,DIG.46 ;118/61,75 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Barnebey-Cheney, Columbus, OH, Activated Carbon Purification &
Recovery Equipment, "Adsorption Equipment for Air Pollution
Control," pp. 1-4. .
Barnebey-Cheney, Columbus, OH, "Series F FilterFold Adsorber," pp.
1-4. .
Max K. Carthew, "Special Report Pollution Control: Controlling
Paint Fume Emissions," Industrial Finishing, Apr. 1983, pp. 28-29.
.
"Carbon Adsorption," pp. 30-31. .
Baron-Blakeslee, Inc., Melrose Park, IL, 4 pp. .
Bildon Industries, Inc., Lake Geneva, WI, advertisement, Industrial
Finishing, Jun. 1983, p. 52..
|
Primary Examiner: Spitzer; Robert
Attorney, Agent or Firm: Leydig, Voit & Mayer, Ltd.
Claims
I claim:
1. In an industrial painting system including a spray booth and a
bake oven, a method for the removal and disposal of the paint
solvent contained in the spray booth exhaust gas discharged from
the spray booth comprising,
(a) passing solvent laden exhaust gas from said spray booth through
a filter capable of adsorbing said solvent from said spray booth
exhaust to remove said solvent from said exhaust;
(b) degassing said filter by passing through said filter a gas such
that the pressure drop across said filter is less than about six
inches of water, said gas having a velocity and temperature
sufficient to remove said solvent from said filter such that the
solvent concentration in the gas exhausted from the filter does not
exceed the lower explosive limit for the solvent;
(c) introducing said filter exhaust to said bake oven to increase
the solvent concentration in the bake oven atmosphere; said
degassing gas velocity and temperature being so selected that upon
introduction of said filter exhaust to said bake oven, the solvent
concentration in the bake oven does not exceed the lower explosive
limit of the designed theoretical level of operation of the brake
oven;
(d) removing a portion of the atmosphere of the bake oven from the
bake oven and incinerating said bake oven atmosphere so as to
oxidize said solvent to non-polluting combustion products and
thereby dispose of said solvent.
2. The method of claim 1 wherein said bake oven atmosphere is
incinerated in a washer having a burner, and whereby the solvent
provides a supplement to the fuel requirement of the burner.
3. The method of claim 1 wherein said industrial painting system
includes a drying oven suitable for drying a wet work piece and the
gas for degassing the filter is provided by the exhaust from said
drying oven.
4. The method of claim 1 wherein said degassing gas temperature is
in the range of from about 100.degree. F. to about 280.degree.
F.
5. The method of claim 1 wherein said filter is activated
carbon.
6. The method of claim 1 wherein the flow of said degassing gas is
co-current with said adsorption flow.
7. The method of claim 1 wherein the flow of said degassing gas is
counter-current to said adsorption flow.
8. In an industrial painting system comprising a washer having a
burner, a dry-off oven, a spray booth and a bake oven, a method for
the removal and disposal of the paint solvent contained in the
spray booth exhaust gas discharged from the spray booth, comprising
passing solvent laden exhaust from said spray booth through a
solvent concentrating means to remove solvent from said exhaust and
to concentrate said solvent, removing the solvent from said
concentrating means by passing through said concentrating means a
gas such that the pressure drop across said concentrating means is
less than about six inches of water, said gas having a velocity and
a temperature sufficient to remove said solvent to form a solvent
laden gas such that the solvent concentration in said solvent laden
gas does not exceed the lower explosive limit for the solvent,
introducing said solvent laden gas to the bake oven to increase the
solvent concentration in the bake oven atmosphere said gas velocity
and temperature being so selected that upon introduction of said
solvent laden gas to said bake oven the solvent concentration in
the bake oven does not exceed the lower explosive limit of the
designed theoretical level of operation of the bake oven,
introducing a portion of the solvent laden atmosphere of the bake
oven to the burner of the washer to incinerate the solvent, and
passing the gasses produced by the incineration of the solvent to
the dry-off oven to form the atmosphere of the dry-off oven.
9. The method of claim 8 wherein the solvent concentrating means is
an activated carbon filter.
10. The method of claim 9 wherein the gas passing through said
filter has a temperature of from about 100.degree. F. to about
280.degree. F.
11. The method of claim 9 wherein the gas passing through said
filter to remove solvent is co-current with the solvent
concentrating flow.
12. The method of claim 9 wherein the gas passing through said
filter to remove solvent is countercurrent to said solvent
concentrating flow.
13. The method of claim 8 wherein at least a portion of the dry-off
oven atmosphere is passed to said solvent concentrating means to
remove solvent therefrom.
Description
The present invention relates to systems and method for the
incineration of combustible waste products contained in exhaust
gases discharged into the atmosphere. The system and method of the
present invention are particularly suited to industrial painting
systems.
It is conventional practice in industry today to paint parts to be
used in the assembly of consumer products and industrial machines
in a continuous and automated system. The parts are generally of
metal, although they may be of other materials such as plastic, and
the parts are mounted on an overhead conveyor on hangers and
transported through the system. Such parts may first be cleansed in
a washer, and thereafter transported through a dry-off oven to
remove moisture from the parts. After the parts have been dried,
they are transported to a spray booth, where paint is applied to
the parts. Finally, the parts may be transported to a bake oven
where the parts are heated to volatilize the solvent of the paint
and to cure the paint to a thin dry film of pigment on the article
or part being processed. The washer, dry-off oven, spray booth, and
bake oven can be operated as a batch system in which the parts
remain at rest during processing, or they may be utilized with a
continuously moving conveyor in a continuous process. High volume
production and low cost production generally dictate the use of a
continuous process.
In the continuous painting processes presently used, the solvent
from the paint is discharged into the atmosphere and thus is an air
pollutant. Approximately 20% of the solvent from the paint is
removed in the bake oven, and industry has frequently discharged
such solvents to the atmosphere, causing a pollution problem and a
loss of thermal energy. About 70% of the solvent lost in an
industrial painting system occurs in the spray booth. The solvent
in the atmosphere of the spray booth becomes contaminated and large
quantities of air are caused to flow through the spray booth to
remove the solvent from the spray booth for purposes of human
safety and to prevent explosion. In the past, the quantities of air
used to cleanse the spray booth were also exhausted to the ambient
atmosphere. The remaining approximately 10% of the solvent lost in
the industrial painting process is lost to the rooms in which the
painting occurs, and this atmosphere also is exhausted to the
ambient surroundings by ventilation systems.
It has long been recognized that the solvents which evaporate from
paint in an industrial painting process can be burned in a flame
incinerator, and since the solvents are hydrocarbons, the oxidation
of these hydrocarbons will reduce the solvents to water (H.sub.2 O)
and carbon dioxide (CO.sub.2). U.S. Pat. No. 3,472,498 of Price et
al. entitled AIR POLLUTANT INCINERATOR, Oct. 14, 1969, describes
the prior art at that time and seeks to provide an improved
apparatus for incinerating paint solvents from the bake oven in an
industrial painting system. Specifically, Price utilizes a
particular incinerator and blower construction coupled to the
atmosphere of the bake oven, in order to incinerate fumes in the
bake oven, and Price introduces cooling air between the incinerator
and a blower for the purpose of reducing the temperature to permit
the incinerated air to be transmitted to the dry-off oven and
returned to the bake oven in specific portions.
Incinerators themselves for disposing of the fumes of paint are
also disclosed in U.S. Pat. No. 3,875,678 to Vits entitled METHOD
AND APPARATUS FOR PURIFYING EXHAUST AIR OF A DRYER APPARATUS. The
large quantities of flue gases which must be subjected to an
afterburner and the high temperature of the gases from the
afterburner are described in the Vits patent as deleterious, and
Vits utilizes the exhaust heat from the afterburner or incinerator
to heat a heat carrier (thermo-oil) which is supplied to the dryer
for heating its atmosphere.
The art also contains a number of specific incinerator
constructions, such as U.S. Pat. No. 4,354,440 of McRee, Jr.
entitled UNDER FIRE AIR AND STEAM SYSTEM AND INCINERATING PROCESS
FOR A CONTROLLED STARVED-AIR INCINERATOR which produces steam from
waste materials, U.S. Pat. No. 4,331,630 of Van Pool entitled
APPARATUS FOR INCINERATION OF SULFUR PLANT TAIL GAS, and U.S. Pat.
No. 3,780,674 to Liu entitled LIQUID INCINERATOR. These patents do
not disclose any particular utility for the incinerators thereof
with respect to an industrial painting system.
The industrial painting systems of the prior art which utilized an
incinerator have limited the use of the incinerator to the bake
oven or curing oven. Only 20% of the solvent is actually removed in
the curing oven, while about 70% of the solvent evaporates in the
spray booth and is typically exhausted into the atmosphere. It is
thus a primary object of the present invention to reduce pollution
of the atmosphere caused by the high solvent containing exhaust of
from the spray booth by first concentrating the solvent from the
spray booth atmosphere in a solvent concentrating means,
controlling the release of the solvent from the solvent retaining
means to desired concentrations, and subsequently burning the
released solvent.
Insurance requirements dictate that large quantities of air flow
through the bake oven of an industrial painting system in order to
limit the level of solvent to air to safe levels. Approximately
10,000 standard cubic feet of air must flow through the bake oven
for each gallon of common paint solvent that is evaporated. In the
prior art industrial painting systems, large quantities of heated
air are exhausted to the atmosphere with a loss of thermal
efficiency to the system. It is, accordingly, an object of the
present invention to provide an industrial painting system that
significantly reduces the amount of air and heat which must be
exhausted to the atmosphere from the bake oven, and it is a further
object of the present invention to provide a complete system of
washer, dry-off oven, spray booth and bake oven which will exhaust
relatively little air to the atmosphere and will exhaust to the
atmosphere relatively little heat from the process. It is
accordingly an object of the present invention to provide an
integrated system of washer, dry-off oven, spray booth, and bake
oven which utilizes significantly less heat than such a system of
the prior art.
In order to reduce solvent contamination of the spray booth
surroundings and to maintain the atmosphere within the spray booth
with a sufficiently low solvent content, it is necessary to
circulate large quantities of air through the spray booth.
Typically, 70% of the solvent vapors which are generated by the
industrial spraying system will occur in the spray booth and these
solvent vapors are exhausted to the atmosphere by the air
circulating through the spray booth.
In accordance with one aspect of the present invention, a separate
circulation of air is maintained from the atmosphere, through the
spray booth and as the air is exhausted from the spray booth,
through a solvent concentrating means or filter. The filter is
effective to remove solvent from the air circulated through the
spray booth, and the filtered air is exhausted from the filter to
the atmosphere essentially free of solvent vapors.
Air filters are well known, and a number of commercially available
materials are used to adsorb solvent contaminents from air. Among
these materials are carbon, silica gel, activated alumina,
molecular sieves and certain clays. Most effective of these
materials is generally considered to be activated carbon, that is,
carbon which has been subjected to steam in order to provide voids
within the carbon. Such products are commercially available, and it
is known that activated carbon will adsorb hydrocarbons
efficiently, and can be degassed by a flow of hot air.
It is also known that hydrocarbons are released from an activated
carbon filter roughly in the order of their molecular weight if the
filter is subjected to a flow of heated air at a temperature
between 100.degree. F. and 160.degree. F. If air at a temperature
about 160.degree. F. is utilized to degas a hydrocarbon loaded
activated carbon filter, the hydrocarbons tend to be released
simultaneously regardless of molecular weight.
Prior to the present invention, degassing of an activated carbon
filter loaded with hydrocarbons resulted in an initial release of
large quantities of hydrocarbons followed by a declining release
until the filter became degassed. The initial release of large
quantities of hydrocarbons is unsatisfactory for the method and
system of the present invention because the presence of high levels
of vapor hydrocarbons possess the danger of explosion, and further
because large concentrations of hydrocarbon vapors in the
incinerator modify the operating conditions of the incinerator and
the release of heat with time for the incinerator. Accordingly,
another aspect of the present invention provides a method for
degassing a filter loaded with hydrocarbons under which the rate of
release of the hydrocarbons is controlled over a prolonged period
of time.
Thus, in accordance with the present invention, the solvent vapors
trapped by the filter are concentrated by the controlled release of
the solvent from the filter by adjusting the rate of gas flow
through the filter and the temperature of the gas used for
degassing. While a variety of gases may be suitably employed, such,
for example as nitrogen, argon or the like, air is preferably
employed for its economy and availability. Hereinafter the method
of the present invention will be described using air but it should
be understood that other gases may likewise be used.
The desired air velocity and temperature of the air passed through
the filter for degassing are so selected that the solvent
concentration in the air exhausted from the filter does not exceed
the lower explosive limit for the solvent. The solvent may then be
disposed of by incineration or the like.
In the preferred embodiment, when a bake oven for curing the
painted part is employed, the solvent laden filter exhaust air is
circulated to the bake oven and the bake oven exhaust is then
burned in an incinerator, such as a washer or the like. When the
solvent laden filter exhaust air is fed to the bake oven, the air
velocity and air temperature of the air used for filter degassing
are so selected that the concentration of solvent in the exhaust
from the filter, when combined with the atmosphere of the bake
oven, is such that the total solvent concentration in the bake oven
does not exceed the lower explosive limit of the designed
theoretical level of operation. Typically, the total solvent
concentration in the bake oven is designed to be about 20% of the
lower explosive limit.
Suitable air degassing velocities may vary over a wide range and
should be selected such that the pressure drop across the filter is
less than about six inches of water.
Suitable air degassing temperatures are in the range of from about
100.degree. F. to about 280.degree. F. It is contemplated that air
from the dry-off oven will be used to degass the filter without any
additional energy requirements since the exhaust air from the
dry-off oven is often in the range of about 200.degree. F. to
400.degree. F. If the dry-off oven exhaust air is too high, for
example greater than about 270.degree. F. or so, it may be
necessary to dilute it with ambient air to cool the dry-off oven
exhaust air to the temperature desired for degassing.
In many applications it may be desirable to utilize a second filter
identical to the first to remove the solvent from the air in the
spray booth during periods in which the first filter must be
degassed. Thus, the first filter will be degassed within the time
period required for loading the second filter with solvent. Hence,
the alternate use of two identical filters of adequate capacity
will result in a continuous operation, and there will be no burst
of solvent vapors from the degassing process that will require
special precaution to prevent explosion or impose load requirements
on the incinerator.
In accordance with a further aspect of the present invention, the
burner of the washer is utilized as the incinerator for fumes from
the bake oven. In one form of conventional washer, a large tank of
water is provided with a tube submerged therein, and the tube is
heated by a flame from a burner fed with natural gas. Water from
the tank is then circulated through sprayers to impinge upon the
items being processed and thereafter returned to the tank for
further heating. By mixing the solvent laden air from the bake oven
with the fuel feeding burner, the solvent is oxidized within the
flame to CO.sub.2 and water. It will be appreciated that the
solvent forms a supplement to the fuel feeding the burner thereby
reducing the fuel requirement for the system.
Further, the region of the tube between the flame and the exit end
of the tube functions as a heat exchanger to transfer the heat from
the flame to the water in the tank, and therefore the gases
emerging from the exit end of the tube are at a reduced temperature
of approximately 450.degree. to 600.degree. F., and are further
substantially oxygen free. Hence, these gases may be used directly
to provide heat for the dry-off oven or the bake oven without
cooling.
The quantity of air which may be transferred from the bake oven to
the burner of the washer is limited by the capacity of the burner,
but in practice it is sufficiently large to provide 10,000 standard
cubic feet of air per minute for each gallon of solvent that is
evaporated. The atmosphere within the bake oven is confined by the
walls of the oven and by air seals operating at the inlet opening
and exit opening of the oven, these air seals being effective to
prevent the introduction of the ambient atmosphere into the oven
during operation, and to confine the atmosphere within the bake
oven. Air seals of the type disclosed in the inventor's U.S. Pat.
No. 4,298,341 entitled INDUSTRIAL OVEN HAVING AIR RECIRCULATING
MEANS FOR MINIMIZING HEAT LOSS granted Nov. 3, 1981, are effective
for this purpose. As noted above, solvent laden air from the
solvent concentrating means is circulated through the bake oven
such that the amount of solvent introduced into the bake oven
increases the solvent concentration in the atmosphere of the bake
oven to not greater than 20% of the lower explosive limit of the
solvent in order to prevent explosion and to comply with operating
government regulations. This is typically the designed solvent
capacity of the bake oven. This solvent concentration is so
maintained by providing an adequate flow of air through the bake
oven, and if a washer is used, the burner of the washer is capable
of accepting that entire flow.
Further, since the temperature of the exhaust gases from the tube
of the washer/incinerator are at a relatively low temperature, such
as 400.degree. F., these exhaust gases are directly usable in the
dry-off oven. The dry-off oven is also provided with air seals at
the inlet opening and exit opening in order to confine the
atmosphere within the dry-off oven. Since the washer burner
requires additional combustion air to that from the bake oven and
natural gases to burn, a portion of the gas flow from the dry-off
oven may be transported directly to the bake oven to provide the
make-up air required to balance the flow of solvent vapor
containing air from the bake oven to the washer/burner. A portion
of the gasses from the dry-off oven is also exhausted to the
atmosphere, and since the atmosphere of the dry-off oven is of
relatively low temperature and free of solvent contamination, the
exhaust to the atmosphere is non-polluting and removes little heat
from the system.
The present invention will be more fully and completely understood
with reference to the following drawings, in which:
FIG. 1 is a diagrammatic view of an industrial painting system and
apparatus according to the present invention;
FIG. 2 is a diagrammatic view of the spray booth solvent control
system according to the present invention;
FIG. 3 is a longitudinal sectional view of a bake oven;
FIG. 4 is an isometric view of a parts washer for use in the
present invention; and
FIG. 5 is a sectional view taken along the line 5--5 of FIG. 4.
FIG. 1 illustrates a commercial system in which parts to be painted
are conveyed on a monorail illustrated by the dashed line 10
through a washer 12, dry-off oven 14, spray booth 16, and a bake
oven 18. The completed painted product emerges on the monorail 10
from the bake oven 18.
The washer 12 is generally illustrated in FIG. 4, and it will be
noted that the monorail 10 enters the washer 12 at the upper side
of an opening 20, extends through a passage 21 and exits from the
opposite side of the washer 12 at the upper side of a second
opening 22. Products to be painted are carried on and depend from
the monorail 10 in the manner illustrated in FIG. 3.
The washer 10 is provided with a tank 24 disposed in the lower
portion thereof, below the passage 21. The tank 24 is substantially
filled with water, the water level being indicated by the dashed
line 26. Beneath the surface of the water in the tank 24 is a
serpentine tube 28 which enters through a first port 30 and exits
through a second port 32. (FIG. 5) A burner 34, preferably fueled
by natural gas, is disposed exterior of the tank 24 and
communicates with the port 30 to produce a flame 36 which extends a
substantial distance down the tube 28. In this manner, the water 25
surrounding the tube 28 is heated, and the water in the tank 24 is
transported to apertured tubes 38 which line the passage 21 through
tubing and a pump 40. The apertured tubes 38 line both sides of the
passage 21, although FIG. 4 illustrates only a few such tubes 38
for clarity. As a result, water is pumped into the passage 21 to
spray against the parts of the work load as they travel down the
monorail 10 to cleanse the parts.
After the parts are cleaned, they enter the dry-off oven 14 where
the parts are dried. The parts continue to be carried on the
monorail out of the dry-off oven 14 and into the spray booth 16. In
the spray booth, a layer of paint is applied to the parts. The
parts then leave the spray booth 16, the paint remaining wet, and
enter the bake oven 18. In the bake oven 18, the paint is cured or
dried, to produce a baked paint finish on the parts. The parts
leave the bake oven 18 with a hard paint finish.
Since the dry-off oven 14, and bake oven 18 are provided with inlet
openings and exit openings for the monorail 10 and parts carried by
the monorail, it is necessary to provide seals for these openings
in order to control the atmosphere within the dry-off oven and bake
oven. It may be desirable to control the atmosphere of the washer
12 for the purposes of economizing on heat and to prevent moisture
from entering the surroundings. The warm water vapor used in the
washer 12 does not represent an environmental hazard.
The bake oven 18 operates at a relatively high temperature, i.e.,
about 350.degree. F. in the preferred construction of the present
invention, and it is known that significant heat may be saved by
the use of air seals on the bake oven. To a lesser extent, heat may
also be saved in the dry-off oven by the use of air seals. It is in
any event necessary to control the atmosphere from the bake oven in
accordance with the teachings of this invention in order to reduce
the escape of vapors from the painting process and reduce the
environmental contamination.
The air seal illustrated in FIG. 3 is suitable for use in the
washer 12, dry-off oven 14, and bake oven 18 for both the inlet and
exit openings. The air seal is more fully described in the present
inventor's U.S. Pat. No. 4,298,341.
The construction of the oven 18 is illustrated in some detail in
FIG. 3. The oven has an inlet opening and an outlet opening, FIG. 3
illustrating only the inlet opening 42, the outlet opening being
identical. The oven 18 is heated by a heating system 44 with a
manifold 46 for circulating the heated air. The heating system 44
also has a heat exchanger 48 which is coupled to the interior
chamber 50 of the bake oven 18 through a port 52, and a fan 54
recirculates air from the chamber 50 through the heat exchanger 48
and manifold 44 to distribute the heat within the bake oven 18. The
port 52 is coupled to the fan 54 by a conduit 56, and the conduit
56 has a port 58 which is connected to the dry-off oven 14 by a
tube 60 in order to introduce air and gasses from the dry-off oven
14, as previously described. In addition, the bake oven 18 has a
second port 62 which is connected to the air intake of the burner
34 of the washer 12 through an impeller 64 and a conduit 66.
The air seal, or heat retention means, is illustrated associated
with the inlet opening 42 and designated 68. A nozzle 70 mounted
adjacent to the upper wall 72 of the bake oven 18 adjacent to the
opening 42 in the front wall 74, is connected to a blower 76. The
blower 76 is connected to the chamber 50 of the oven 18 in a region
adjacent to the front wall 74. The nozzle 70 is positioned to blow
the recirculated air from the chamber 50 downward across the inlet
opening 42 and at an angle inwardly therefrom. As described in
greater detail in the present inventor's U.S. Pat. No. 4,298,341,
this construction is effective to prevent the escape of atmosphere
from the chamber 50 to the exterior of the bake oven 18, and at the
same time, the flow of air across the inlet opening 42 is
sufficiently low that parts, designated 78, carried on hangers 80
on the monorail 10 will not be blown from the hangers and will be
permitted to pass through the chamber 50 of the bake oven in an
orderly manner.
The spray booth however is provided with a flow of air from the
ambient atmosphere typically through an opening at the front of the
booth, and is drawn through the booth by a ventilating fan to
provide fresh air to the interior of the spray booth. An exit port
90 (FIG. 2) exhausts the atmosphere from the interior of the spray
booth 16, and the exit port 90 is connected to a blower 94. A
conduit 96 from the blower conducts solvent laden air from the
spray booth to one of two filters 98 or 100. A valve 102 is
connected between the conduit 96 and the filters 98 and 100 to
direct the air from the spray booth 16 to filter 98 or filter 100.
The filters 98 and 100 have outlets connected to a valve 104 which
couples the filters 98 or 100 to ambient atmosphere designated
exhaust.
The spray booth pollution control system is best illustrated in
FIG. 2. Each of the filters 98 and 100 has an air-tight enclosure
106 divided into two compartments 108 and 110 by a layer 112 which
extends centrally across the enclosure 106. The layer 112 comprises
a mass of filtering material, such as activated carbon. The valve
102 is connected to the one compartment 108 of each of the filters
98 and 100.
The compartments 110 of the filters 98 and 100 are not only
connected to the valve 104, but also through a separate conduit to
the heat source or dry-off oven 14. The incinerator or burner 34 is
connected to the valve 102.
In operation, fresh air enters the spray booth 16 and is
continuously flushed through either the filter 98 or the filter
100, depending upon the position of the valve 102. When the valve
102 connects the spray booth 16 to the filter 100, as illustrated
in FIG. 2, solvent vapors from the paint in the spray booth are
deposited on the activated carbon layer 112 of the filter 100 as
the air flows through the filter 100 and the valve 104 to exit into
the atmosphere.
During a previous operating cycle, the filter 98 was coupled to the
spray booth by the valve 102 and has been loaded with paint
solvent.
In the embodiment of FIGS. 1 and 2, solvent laden air from the
spray booth passes through the filters 98 or 100 in one direction,
and degassing air from the heat source 14 passes through the
filter. Preferably, for optimum operation, degassing air is passed
through the filter in the direction opposite to that which the
filter was loaded. The reverse flow of air through the filter has
the effect of further limiting the initial evolution of vapors from
the filter in order to produce a relatively constant evolution of
vapors over a prolonged period of time. The filter of course may be
degassed in the forward direction as well as the reverse direction,
but with an increase in the initial evolution of vapors. As stated,
the temperature of the air from the heat source 14 is between
100.degree. F. and 280.degree. F., and the air velocity is such
that the pressure across the filter is less than about 6"
water.
As illustrated in FIG. 1, air from the spray booth 16 is connected
to filter 98 through the valve 102 and to the exhaust through the
valve 104. Also, filter 100 is in the process of degassing, and the
valve 114 has connected the dry-off oven 14, functioning as the
heat source, to filter 100, and valve 102 has connected filter 100
to the incinerator through the bake oven 18. Valves 102, 114, and
104 are preferably ganged together so that switching of the valves
to their opposite position will produce the connections shown in
FIG. 2 in which the spray booth is connected to filter 100 and
filter 98 is being degassed.
In the degassing process, valve 102 connects the filter 98 or 100
to the bake oven 18, thereby mixing the vapors of degassing from
the filter with the atmosphere of the bake oven. This has the
effect of averaging the vapors from the filter to provide a
relatively constant volume of vapors to the burner of the washer 12
for incineration. A vapor control unit 116 monitors the level of
solvent vapors in the bake oven, and if this level exceeds the
threshold value earlier described, the vapor control opens valve
118 to permit fresh air to be mixed with air from the dry-off oven
14, thereby providing a lower temperature air to the pump 120. As a
result of lowering the temperature used for degassing filter 100,
the quantity of vapors entering bake oven 18 will be reduced.
As illustrated in FIG. 5, the serpentine tube 28 is provided with a
valve 122 and a bypass tube 124 to effectively shorten the length
of the tube. The flame 36 in the tube of the incinerator extends
for a distance of between five and twenty feet, and the valve 122
is located down stream from the end of the flame. The tube 28 acts
as a heat exchanger, not only in the region in which the flame
exists, but in the region from the end of the flame to the outlet
port 32. By shortening the length of the path of the hot gasses
from the flame 36 by means of the bypass 124, the amount of heat
transferred from the flame 36 to the water 25 in the tank 24 is
reduced, and the temperature of the gasses emerging from the exit
port 32 are increased. In this way the temperature of the body of
water 25 in the tank may be reduced, and the parts washed in cooler
spray. On the other hand, the temperature of the dry-off oven 14 is
increased by utilization of the bypass 124, and, air from the
dry-off oven may be used to degass the filters without the need for
additional heating of the atmosphere of the dry-off oven. The valve
122 may therefore be utilized to control degassing of the filters
98 and 100.
Those skilled in the art will devise many modifications and uses
for the present invention above than set forth in this
specification. It is therefore intended that the scope of the
present invention be limited not by the foregoing specification,
but rather only by the appended claims.
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